Lumber spinal stenosis refers to a medical condition in which the spinal canal or neural tube that encompasses the spinal cord is compressed by a bone or ligament enlarged due to a degenerative change. Such an enlarged bone or ligament presses the nerve that passes through the lumbar spinal canal, thereby causing low back pain or leg pain. Although non-surgical treatment may be performed as a primary treatment, spinal stenosis not responding to non-surgical treatment for a certain period of time can be treated fundamentally only by a surgical operation. Therefore, surgical treatment must be considered in patients who have diseases that have progressed considerably and thus do not show any significant effect by conservative therapies, or patients who have many limitations in daily lives or have acute severe symptoms accompanied by a disc disease.
Examples of the surgical methods of treating the disease may include an intervertebral fusion which uses an intervertebral implant cage and a posterior pedicle screw. The intervertebral fusion often results in removal or destruction of several vertebral elements, such as the lamina and spinous process, and may thus cause structural deformations of the vertebrae and instability of the respective parts. Additionally, since the intervertebral fusion surgery completely restricts the motion of the treatment site, the procedure relatively increases the motion of the adjacent segments and may thereby accelerate the degeneration of the lumbar spine.
An exemplary surgical method to remedy the problem of the intervertebral fusion may be a method of expanding the nerve space under compression by inserting a device between interspinous processes of vertebrae. This method may be used instead of the existing method of removing vertebral bones or discs for the purpose of releasing the compressed nerves. In particular, the device inserted between interspinous processes of vertebrae is an intervertebral spacer and also called interspinous spacer. This method is a surgical method suitable for those patients who have a symptom that becomes severe when bending their waist backward while the symptom is alleviated when bending their waist forward. Upon insertion of the spacer, the ligament or disc that had invaded the intervertebral space is straightened, and thus the nerve-compressing phenomenon is resolved. In addition, with regard to disc diseases in which the disc height is reduced, the neuropores can be widened and thus the method has an effect of preventing spinal stenosis that may occur after simple decompression surgery.
The intervertebral spacer may be manufactured using a material such as metals, ceramics, polymers, etc. The material for the intervertebral spacer may be selected considering strength, durability, biocompatibility, in vivo stability, in vivo non-toxicity, easy processability, disinfection/sterilization stability, etc. Additionally, it is important that the material is provided with magnetic permeability, radiolucency, and appropriate hardness. A metal such as titanium, etc. have excellent biocompatibility and strength, but it has an extremely high modulus of elasticity, and thus may cause a stress shielding effect and also causes an interference phenomenon in response to a strong magnetic field such as MRI, etc., thereby making it difficult to perform a follow-up surveillance after surgery. Meanwhile, polymers such as PEEK have advantages in that they have high-strength, a low risk of fracture, and an appropriate modulus of elasticity but has a disadvantage in that they have significantly low biocompatibility compared to ceramics or metals such as titanium, etc. Ceramics such as hydroxyapatite (HA), bioglass, etc. have high biocompatibility but have low strength and a high risk of fracture, and thus it may be difficult to solely use them.